In multiple completion wells, a cased borehole traverses one or more vertically spaced oil production zones or strata in the earth strata. The borehole is lined and cemented in place with a casing and two or more of the vertically spaced strata are perforated for completion. The production from each of the strata is independently conveyed to the earth's surface by separate strings of tubing where the respective strings of tubing respectively extend to each of the producing strata. The producing strata are separated from one another by packer means. Thus at the very minimum there is a "long" string of tubing which extends through an upper packer located above an upper oil producing zone and extends through a lower packer which is located between the upper producing zone and the lower producing zone. The long string of tubing thus provides in independent flow conduit from the lower production zone through the upper production zone to the earth's surface. A "short" string of tubing extends from the earth's surface through the upper packer and opens to the upper production zone so that hydrocarbons are independently produced from the upper production zone to the earth's surface.
During the installation of the packers and strings of tubing and prior to production, the well casing is commonly filled with a weighted well control liquid commonly called "mud" which provides a hydrostatic pressure greater than the pressure of the fluids in the formations. Thus, the long and the short strings of tubing and the packers are installed with the existence of mud in the casing and the mud enters into the bores of the strings of tubing. The upper packer in a dual flow completion system ordinarily accommodates the two strings of tubing and the lower packer accommodates a single string of tubing. It is necessary for production to reverse out or remove the mud from a string of tubing. While there are various ways to do this, it is common to use a circulation valve in the string of tubing. The circulation valve is normally closed and is opened by a wire line tool so that fluid pressure in the annulus about a string of tubing can be used to reverse out the mud in a string of tubing.
There are a variety of systems used for controlling various pressure and gas conditions existent in the upper and lower production zones. Irrespective of the system in dual completions and in single completions as well, it is necessary to reverse out or circulate out the mud in the casing and in the string of tubing to the earth's surface. Usually the mud is replaced with a lighter weight liquid.
In U.S. Pat. No. 3,791,449, a system is shown where the long string of tubing has a pressure operated sleeve extension at its lower end. Thus when the upper packer is in position above the upper strata, the sleeve extension at the lower end of the long string of tubing remains open above the upper packer so that liquid can be circulated from the long string through the casing and to the earth's surface via the short string of tubing. Upon completion of the circulation operation, the extension sleeve on the long string of tubing is actuated to move downwardly into sealing engagement in a bore in the lower packer to complete the hookup. The extension sleeve in the long string of tubing is operated by dropping a ball and moving the extension sleeve under pressure to an extended position where it is locked in place by a one way clutch member in the lower packer. The ball is removable by pressure to discharge to the bottom of the well.
In U.S. Pat. Nos. 3,882,936 and 3,799,268, a circulating valve is located in a long string of tubing above the lower packer while the long string is connected to the lower packer. The circulating valve includes interconnected sleeves on a tubular body member where a circulating port is closed by the sleeves and the other sleeve is pressure balanced by pressure ports opening to equal and opposite effective pressure areas. When the long string is sealed in the sealing position in the lower packer member, an increase of pressure in the tubing string causes pressure in the circulating ports to disengage one of the sleeves from the other sleeve and the circulating ports are opened to the casing so that liquid can be circulated from the interior of the long string of tubing through the short string of tubing. When it is desired to close the circulating ports after circulation operation has been completed, a ball member is dropped into the string of tubing to separate the pressure ports providing the pressure balance on the other sleeve so that a pressure in the string of tubing above the scaling ball will cause the other sleeve member to slide axially and join with the one sleeve member to close the circulating ports.
In some dual well completions, it is customary to utilize wire line actuated circulating valves which require the time and use of a wireline crew and wireline tools. In many instances, well operators do not wish to utilize circulating valves requiring wireline operations. There is a need for pressure operated circulating valves particularly for dual flow completions.
Dual well completions, as discussed involve a control fluid (mud) in the casing to control the well pressure of the production zones. With upper and lower production zones, either zone may be higher in pressure. There are many instances where the differences in pressure in the production zones create a circulation problem for use of either the long string or short string. Thus, a circulation valve may be used in both long and short strings. Also, while dual production has been discussed it is common to use circulation valves in a single string.